Metal detectible ceramic material and method for making the same

ABSTRACT

A method for producing a cermet composition, including mixing a first predetermined amount of a yttria stabilized zirconia powder with between 2 and 8 weight percent mu-metal powder to define a homogeneous admixture, oxidizing the mu-metal in the admixture, forming the homogeneous admixture into a green body, calcining the green body in a first reducing atmosphere to remove oxygen from the oxidized mu-metal to yield a calcined body, and sintering the calcined body in a second reducing atmosphere to yield a densified body having no more than 0.8% porosity. The densified body has a plurality of mu-metal particles distributed therethrough, a hardness of at least 1450 HV, flexural strength of at least 200 kPSI, and a relative permeability μ/μ o  of at least 850.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of, and claims priority to, co-pending U.S. patent application Ser. No. 13/890,743, filed on May 9, 2013, which claimed priority to then co-pending U.S. provisional patent application Ser. No. 61/644,610, filed May 9, 2012, and to then co-pending U.S. provisional patent application Ser. No. 61/752,086, filed Jan. 14, 2013; and is also a continuation-in-part of, and claims priority to, co-pending U.S. patent application Ser. No. 14/192,815, filed on Feb. 27, 2014, which claimed priority to then co-pending U.S. provisional patent application Ser. No. 61/770,269, filed on Feb. 27, 2013.

TECHNICAL FIELD

The novel technology disclosed herein relates generally to the field of ceramic materials and, more particularly, to a theoretically dense sintered ceramic material that exhibits strong paramagnetic and/or ferromagnetic properties.

BACKGROUND

Tooling involved in the production of food and pharmaceuticals is typically metallic. Although ceramic materials have superior compressive properties, they are brittle and tend to chip. Thus, ceramic tooling is considered unsuitable for use with food and/or pharmaceuticals, since ceramic chips or fragments are difficult to detect and can contaminate the foodstuffs and/or pharmaceutical materials. Thus, there remains a need for ceramic tooling enjoying superior compression strengths along with easy detection of chips and fragments for screening and removal. The present novel technology addresses this need.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side plan view of a piston assembly according to a first embodiment of the present novel technology.

FIG. 1B is a side cutaway view of the embodiment of FIG. 1A.

FIG. 1C is top plan view of the mandrel portion of the piston assembly embodiment of FIG. 1A.

FIG. 2A is a front perspective view of the embodiment of FIG. 1A.

FIG. 2B is a partial side cutaway elevation view of the embodiment of FIG. 1A.

FIG. 3 is a side cutaway elevation view of the embodiment of FIG. 1A.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of the novel technology and presenting its currently understood best mode of operation, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the novel technology is thereby intended, with such alterations and further modifications in the illustrated device and such further applications of the principles of the novel technology as illustrated therein being contemplated as would normally occur to one skilled in the art to which the novel technology relates.

The present novel technology relates to ceramic or cermet compositions that may be formed into sintered and densified ceramic bodies that enjoy the physical toughness, strength and wear resistance of ceramics while being detectible by conventional metal detection techniques. These cermet compositions may then be formed into such bodies as metal-detectible ceramic tooling or the like, thus offering improved safety features by increased ability to detect any small contaminate.

In one embodiment, the cermet composition includes a ceramic matrix phase such as ZrO₂, yttria stabilized zirconia (YSZ), Gd₂O₃, and combinations thereof, with a metallic phase such as Ni, Fe, Co, permalloy, Mu-metal, and combinations thereof, dispersed therein. The metallic phase is typically introduced in oxide form for reduction to metallic form during processing, to avoid mixing issues arising from significant density differences as well as metallic species chemically interacting with oxide species at elevated temperatures.

The metallic phase may be an alloy, and the alloy may be introduced as metal alloy particles, particles of oxidized alloy, or as oxides of the constituent metals for reduction and subsequent alloying of the resulting metals. The metallic phase typically has a high magnetic permeability μ of at least about 1×10⁻⁴ H/m with a relative permeability μ/μ_(o) of at least about 100, more typically μ being at least about 5×10⁻³ H/m and μ/μ_(o) at least about 4000, still more typically μ being at least about 1×10⁻² H/m and μ/μ_(o) at least about 8000, and yet more typically μ being about 2.5×10⁻² H/m and μ/μ_(o) 20,000. In some cases, μ/μ_(o) may exceed 50,000 or more.

Typically, the matrix and metallic phase materials are provided as precursor powders, with the metallic phase present in sufficient quantity to yield between about 1 volume percent and 20 volume percent metallic particles to the resultant cermet body, with about 80 to about 99 volume percent of the powder giving rise to the ceramic matrix phase, and with about 1 to about 8 weight percent of organic additives. A typical composition has less than 10 volume percent of the powder that gives rise to the metallic phase, with the balance being given to the powder giving rise to the ceramic matrix phase and, optionally a small amount of organic additives. If the powder giving rise to the metallic phase is a reducible material (e.g., a metal oxide), the volume percent of initial precursor powder is typically appropriately adjusted to compensate for the loss of the species (e.g., oxygen) that is removed during firing in a reducing atmosphere.

Typically, the matrix phase is a stable, structural ceramic, such as ZrO₂, yttria stabilized zirconia (YSZ), Gd₂O₃, or the like, and may include such materials as the various stabilized zirconias, zirconia-toughened alumina, alumina, TiB₂, ZrB₂, HfB₂, TaB₂, TiC, Cr₃C₂, and the like, and mixtures thereof.

The cermet composition may be prepared by any process that yields a monolithic part, typically having a well-blended mixture of the ceramic matrix phase and the oxide precursor phase, that will yield the metallic phase upon firing in a reducing environment. This may include preparation by slip casting, extrusion, freezing, and the like. One typically selected method is dry pressing, such as uniaxial pressing, cold isostatic pressing, hot isostatic pressing, and the like.

The appropriate powder preparation method is dictated by the selected method for processing the cermet composition. Dry pressing the powder giving rise to the ceramic matrix phase and the powder giving rise to the metallic phase are homogenized through mixing/blending to define an admixture. Additionally, organic additives such as surfactants, binders and the like may be present in small amounts to aid in powder processing, green body formation, and the like. Typically, these organic additives may be dissolved in a suitable liquid to be gradually added to the mixed inorganic powders in a shear granulation process. One typical powder preparation method includes preparing a suspension of the mixed inorganic powders and organic additives for drying to yield press ready granules.

In the case of an oxide powder precursor for yielding a metal alloy phase (i.e., a metal consisting of more than one element), it is preferred that the multiple oxide powders be calcined together at suitably high temperatures to generate a multi-elemental reaction product that is subsequently milled to a particle size that is appropriate for subsequent powder processing. Alternatively, predetermined amounts of constituent metals may be mixed and fused, with the fusion product allow later milled into a metallic powder precursor to yield an admixture.

The homogeneous admixture is then formed into a green body. Typically, the admixture is introduced into a mold and pressed into a green body. In some embodiments, small amounts of binder are introduced to assist the green body in retaining its shape after formation. The green body is then sintered at elevated temperatures and under controlled, reducing atmospheric compositions. A majority of the non-matrix metal oxide portion is reduced to yield a sintered cermet body having a predetermined amount of metallic particles dispersed in a sintered ceramic, typically oxide, matrix. In some instances, the admixture is introduced into a mold and then formed directly into a sintered cermet body, such as through a hot isostatic pressing (HIP) technique.

Generally, the admixture is heated at one to ten degrees Celsius per minute until a peak temperature between 1400 and 1700 degrees Celsius is reached. Then the admixture is held at this peak temperature for no greater than four hours. This is followed by a cool down by decreasing the temperature of the admixture between one to 5 degrees Celsius per minute until a temperature between 1200 and 1400 degrees Celsius is reached. The admixture is to dwell in this temperature range for duration of one to six hours. Then the admixture is to be brought down to room temperature at a rate of one to ten degrees Celsius per minute. The admixture may be processed in powder form, or as pressed into body. The metal particle size and distribution is influenced by the firing time and temperature. For example, longer firing times and/or greater firing temperatures typically yield larger metallic particles.

Once a sintered body is produced, it may be further machined into a desired shape. Further, the sintered body, before and/or after machining, may be soaked at an elevated temperature in a reducing atmosphere, such as annealing in hydrogen, to improve its ability to be sensed by a metal detector. Other generally appropriate reducing atmospheres may include a forming gas (i.e., hydrogen blended with an inert gas at various ratios), ammonia, vacuum, and combinations of the like.

In one embodiment, the green body is chemically activated to yield a densified ceramic matrix having a plurality of metallic particles dispersed therethrough.

In one embodiment, the sintered, densified cermet bodies are formed as pill-making tooling. The pill-making tooling enjoys the benefits of ceramic composition, including compression strength, toughness, durability, corrosion resistance, low coefficient of friction, low thermal expansion coefficient, and the like. The tooling enjoys the advantages of the advanced ceramic with the additional ability of being identified by conventional metal detection technology.

Other embodiments of the sintered, densified cermet bodies include equipment and tooling for the processing of foods and beverages, for pharmaceutical manufacture and processing, medical diagnostic devices and tools, military hardware, weapons, metal blades and cutting tools, industrial tooling and machinery, punches and dies, and the like.

In operation, tooling made from the novel cermet material functions similarly to traditional metal tooling, with the exception of typically requiring less lubricant and maintenance. This is advantageous for tooling associated with the production of pharmaceuticals and foodstuffs, such as pills, vitamins, and the like, as there is an associated reduction of discoloration (i.e., black marks) of the final product. Further, the novel cermet tooling is typically formed as a single piece, as contrasted to traditional multipiece tooling (i.e., metal punch having a ceramic tip), and thus the incidence of attached tooling pieces becoming dislodged during use is eliminated.

Typically, a production line utilizing the novel cermet tooling will have metal detectors for detecting and screening tooling chips from product. Typically, metal detectors employ an electric generator for producing an alternating electric field and a magnetometer for detecting magnetic fields. The electric generator produces an alternating electric field which generates eddy currents in electrically conductive materials; the eddy currents give rise to magnetic fields, which may be detected by the magnetometer. The tooling chip contaminants contain electrically conductive metallic particles which react to the magnetometer. Chips are thus removed from product upon detection. In some embodiments, the novel cermet material is sufficiently ferromagnetic as to be magnetically sortable from nonmagnetic product. Further, the novel cermet is advantageous in that, with the proper selection of allow having high magnetic permeability, it has an ability to be detected at smaller sized particles than ferrous tool steel. Thus the novel cermet allows for possible abrasion resistance of up to 4 to 5 times what is allowed by typical tool steel.

The following example is merely representative of the work that contributes to the teaching of the present novel article, and the novel material is not intended to be restricted by the following example.

EXAMPLE 1

This examples relates to a novel method of manufacturing the novel material starting with a Ni/Fe super alloy which is then ground up, milled and mixed with a zirconium ceramic powder to yield a slurry. Wherein the metallic alloy is present in generally sufficient quantities between typically between about 2 and about 8 weight percent of the total (more typically between about 0.5 and about 20 volume percent of resultant cermet body.) The slurry is then spray dried prior to yield a powder precursor, which may be formed into a green body for sintering.

Generally the sintering steps occur in oxygen-free conditions and the ceramic composition may first be calcined by firing in an ambient atmosphere in order to generally remove any organic additives (binders, dispersants, etc.). Burnout is accomplished by slowly heating the ceramic material between the region of 300 to 400 degrees Celsius, then continuing to heat the composition until appropriate temperature (on the order of 900 to 1100° C.) to bisque fire the composition has been reached, thereby imparting some strength. The bisque fired composition can then be heated in a separate step, using the previously discussed heating profile ranges, under vacuum or a reducing atmosphere to convert the reducible component to a metal while simultaneously sintering the cermet.

Alternatively, the ceramic composition may be fired in a single cycle. The binder burnout portion of the cycle is typically performed in air. Typically, the firing atmosphere remains air until a temperature range of between about 900 and about 1100 degrees Celsius, at which point the firing atmosphere is purged of air and replaced with a reducing atmosphere. Typically, waiting until the temperature range of 900 to 1100 degrees Celsius reduces the likelihood of sequential reduction reactions of single metallic elements in a powder that is intended to give rise to a metal alloy phase. Thus, the atmosphere typically remains as a reducing atmosphere for the remainder of the firing cycle, including the cool down phase.

Once the sintered body is produced, it is typically annealed in hydrogen or other appropriate reducing atmospheres to improve its ability to be sensed by a metal detector.

FIGS. 1A-3 illustrate one embodiment of the present novel technology, a plunger piston assembly 10 typically utilized in pumps, motors or other systems that compress solids, fluids, or the like. The plunger piston assembly 10 generally includes a removable wear sleeve portion 30, a mandrel 40, a housing center 50, and a center pin 60. Previously, when all or part of the piston assembly 10 is worn due to significant compressive forces inherent in the compaction process, the worn part(s) of the piston assembly 10 is/are discarded and the worn components are replaced. The plunger piston assembly 10 allows for replacement of the components to quickly put the piston 10 back into service. This may be done multiple times before the piston assembly 10 has to be replaced with new parts. Therefore, the piston assembly 10 reduces the cost of raw materials, labor and transportation costs, as well as the amount of time the compaction machines are down for repair. The techniques described herein may be adapted to any of number of compaction tooling applications. In addition, the piston assembly 10 and replacement method may be used in other similar compaction embodiments to allow for the use and refurbishment of various materials, typically the ceramic sleeve 30, in high-friction environments. An advantage of the disclosed embodiments and methods is the reuse of a highly machined part instead of replacement of the same, wherein it is, only necessary to replace/refurbish the portion of the piston assembly 10 that is worn. As a result, the life of compaction tooling may be significantly increased and/or the cost of reworking and refurbishing the same may be reduced.

A piston/plunger assembly 10 generally contains a housing center 50, an elongated tubular body typically formed from a single piece of material, the body having a first end 53, a second end 55, an outer surface 57, and an inner surface 59 that defines a plunger receiving a center pin 60. The center pin 60, which is typically disposed inside the housing center 50, is typically made from a structural material, such as the mu-metal doped YSZ material described above, although various metals and possibly other materials, such as tool steel or pre-hardened steel, may be employed and generally includes a first component or a center pin base 63, which is a generally cylindrical component having an aperture 65 in the lower end 67 thereof for controlling the position of the center pin 60, and/or affixing the mandrel 40 to the center pin 60, a ceramic tip 71 that forms the wear surface of the center pin assembly 60. The ceramic tip 71 is attached to the center pin base 73 using a mandrel arbor 75, typically made from tool steel, pre-hardened steel, or the like. As illustrated, mandrel arbor 75 is generally cylindrical, but typically includes either a tapered head at an upper end 77 thereof mated with tapered hole in ceramic tip 71, or a square head mated with counterbored hole in ceramic tip 71, so as to provide a positive engagement between mandrel arbor 75 and the ceramic tip 71.

In the known art, the housing 50, center pin 60, and mandrel 40 were typically permanently affixed in a manner that individual components of the piston/plunger 20 could not be removed or replaced. The piston/plunger assembly 10 permits the quick replacement of any of the piston/plunger components (the mandrel 40, a housing center 50, and a center pin 60) at any time, without having to tear apart the pump, through the use of a removable sleeve 30. The removable wear sleeve portion 30 is typically made of a structural ceramic material such as wear resistant ceramic oxides, although any convenient material may be selected, and is generally shaped and sized to snugly fit the dimensions of a standard piston/plunger 20, although the removable wear sleeve 30 may be sized and adapted to fit any piston/plunger.

To assemble the plunger piston assembly 10, the center pin 60 is typically inserted into the removable wear sleeve 30. The housing center 50 is then attached to the center pin 60 and the mandrel 40 is then cinched down and connected to the center pin 60. This assembly 10 allows the piston/plunger 20 to be used until the piston/plunger is worn from use. Once the piston/plunger 20 is worn, the ceramic sleeve 30 may be removed by removing the mandrel 40 with a wrench, thus releasing the ceramic sleeve 30. A new ceramic sleeve 30 may then be placed onto the pre-existing mandrel 40 and cinched back onto the center pin 60. The use of such ceramic components enables reworking and replacement of the worn tool components. The easy to remove mandrel 40 allows for personnel in the field to easily remove the mandrel 40 and replace the worn ceramic or high wear sleeve 30 in the field. Alternatively, the plunger piston assembly 10 may be swapped out and sent back to the manufacturer to be refurbished and reused at a lower cost.

In some embodiments, cermet bodies of the present novel composition are produced by combining 2-8 weight percent mu-metal powder with a balance of ceramic matrix powder, such as YSZ, to yield a homogeneous admixture. The admixture is formed into a body having a desired shape by hot isostatic pressing (HIPPING) at a relatively low pressure, typically between 500 and 1000 PSI, and at temperatures in the 900° C. to 1500° C. range in a reducing environment, such as flowing dry H₂ or forming gas. This process yields bodies having densities of greater than 99% of theoretical (i.e., less than 1% porosity), more typically greater than 99.2% theoretically dense (less than 0.8% porosity), still more typically greater than 99.5% theoretically dense (less than 0.5% porosity); yet more typically greater than 99.9% theoretically dense (less than 0.1% porosity); and still more typically at substantially 100% theoretically dense (substantially 0% porosity). Table 1 illustrates a typical sintering profile.

EXAMPLE 2

YST powder was mixed with oxidized mu-metal alloy to yield a homogeneous admixture having 4 weight percent mu-metal oxide. The powder was pressed into a green body and calcined at 600° C. for 8 hours to debind and remove the oxygen from the mu-metal oxide. The temperature was ramped to 1400° C. and the calcined body was soaked at 1400° C. for 2 hours to sinter. The sintered body was hot isostatically pressed at 900 PSI in a reducing atmosphere (5% hydrogen gas), after which the body was annealed at 1120° C. for 4 hours, and then ramped to room temperature over 5 hours. The body had a density of substantially theoretical (in excess of 99.9 percent dense), hardness of about 1450 HV, flexural strength of about 200 kPSI, and a relative permeability μ/μ_(o) of about 1000.

EXAMPLE 3

YST powder was mixed with mu-metal alloy and a binder to yield a homogeneous admixture having 3 weight percent mu-metal. The admixture was heated in an oxidizing atmosphere to oxidize the mu-metal. The powder was pressed into a green body and plasma sintered at 1400° C. in a reducing atmosphere (dry H₂) for 10 minutes to remove binder and also the oxygen from the mu-metal oxide and sinter the body. The sintered body was allowed to cool to room temperature with the furnace (natural cool down). The body had a density of 99.5 percent theoretical, a hardness of 1470 HV, flexural strength of 204 kPSI, and a relative permeability μ/μ_(o) of 2500.

EXAMPLE 4

YST powder was mixed with mu-metal alloy to yield a homogeneous admixture having 5 weight percent mu-metal. The admixture was heated in an oxidizing atmosphere to oxidize the mu-metal. The powder was pressed into a green body and plasma sintered at 1400° C. in a reducing atmosphere (dry H₂) for 20 minutes to remove the oxygen from the mu-metal oxide and sinter the body. The sintered body was allowed to cool to room temperature with the furnace (natural cool down). The body had a density of 99.2 percent theoretical, a hardness of 1450 HV, flexural strength of 200 kPSI, and a relative permeability μ/μ_(o) of 2500.

EXAMPLE 5

YST powder may be mixed without mu-metal alloy to yield a homogeneous admixture. The admixture may be pressed into a green body and plasma sintered at 1400° C. in a reducing atmosphere (forming gas, dry H₂, or the like) for 10-30 minutes to sinter the body. The sintered body may be allowed to cool to room temperature with the furnace (natural cool down). The body will have a density of between about 99.2 and 99.8 percent theoretical, a hardness of about 1470 HV, a flexural strength of about 200 kPSI, and a relative permeability μ/μ_(o) of between about 850 and 2500.

While the metal, typically mu-metal, composition is typically held under 20%, compositions are envisioned with sufficient metal or mu-metal phase such that the resulting sintered bodies exhibit metallic electrical conductivity. Such bodies would have contiguity or quasi-contiguity of the metallic phase, and would be able to participate in screening of electromagnetic energy. For example, a functioning Faraday cage may be constructed of high-metal phase cermet pieces.

Bodies formed as described above, particularly those sintered in hydrogen, exhibit the characteristics of having smooth and quasi-polished or polishable surfaces, require substantially less lubrication than metal counterparts, wear evenly with substantially reduced chipping and pitting (than metal or conventional YSZ counterparts). Tooling for pressing pills benefits from high wear resistance, reduced pitting, chipping and rut erosion, reducing and/or eliminating retention of surface material and potential for bacterial contamination.

While the novel technology has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It is understood that the embodiments have been shown and described in the foregoing specification in satisfaction of the best mode and enablement requirements. It is understood that one of ordinary skill in the art could readily make a nigh-infinite number of insubstantial changes and modifications to the above-described embodiments and that it would be impractical to attempt to describe all such embodiment variations in the present specification. Accordingly, it is understood that all changes and modifications that come within the spirit of the novel technology are desired to be protected. 

I claim:
 1. A densified cermet body, comprising: a ceramic matrix; and a plurality of high magnetic permeability metallic particles distributed throughout the ceramic matrix; wherein the densified cermet body has a density of at least 99.2% theoretical.
 2. The composition of claim 1 wherein the ceramic matrix is selected from the group consisting of zirconia, yttria stabilized zirconia, zirconia toughened alumina, alumina, gadolinium oxide, and combinations thereof; and wherein the metallic particles are selected from the group consisting of iron, nickel, cobalt, mu-metal, and combinations thereof.
 3. The composition of claim 1 wherein the ceramic matrix is selected from the group consisting of TiB₂, ZrB₂, HfB₂, TaB₂, TiC, Cr₃C₂, and combinations thereof; and wherein the metallic particles are selected from the group consisting of iron, nickel, cobalt, mu-metal, and combinations thereof.
 4. The composition of claim 1 wherein the metallic particles comprise between about 1 and about 20 volume percent of the ceramic composition.
 5. The composition of claim 1 wherein the metallic particles comprise between about 2 and about 8 volume percent of the ceramic composition.
 6. The composition of claim 1 wherein the ceramic matrix is YST, wherein the metallic particles are mu-metal, wherein the metallic particles comprise between 3 and 5 weight percent of the cermet, wherein the cermet body has a porosity of less than 0.5 percent, wherein the cermet body has a hardness of greater than 1450 HV, wherein the cermet body has a flexural strength of more than 200 kPSI, and wherein the cermet body has a relative magnetic permeability of at least
 850. 7. A method for producing a cermet composition, comprising: a) mixing a first predetermined amount of a first ceramic material with a second predetermined amount of a second metal oxide material to define a homogeneous admixture; b) forming the homogeneous admixture into a green body; c) calcining the green body in a first reducing atmosphere to remove oxygen from the second metal oxide; d) sintering the green body in a second reducing atmosphere to yield a densified body having no more than 0.8% porosity; wherein the densified body has a plurality of metallic particles distributed therethrough; and wherein the densified body has a relative permeability μ/μ_(o) of at least
 850. 8. A method of claim 7, wherein the densified body includes about 2 to about 8 weight percent metallic particles; and wherein metallic particles have magnetic permeability of at least about 1×10⁻⁴ H/m and relative magnetic permeability of at least about
 4000. 9. The method of claim 8, wherein the first ceramic material is YSZ; and wherein the second metal oxide is mu-metal.
 10. The method of claim 7, wherein the first ceramic material is selected from the group consisting of zirconia, yttria stabilized zirconia, zirconia toughened alumina, alumina, gadolinium oxide, and combinations thereof; and wherein the second metal oxide is selected from the group consisting of iron oxide, nickel oxide, cobalt oxide, and combinations thereof.
 11. The method of claim 7 wherein during step d) sintering is accomplished by a sintering technique selected from the group comprising hot isostatic pressing and plasma sintering.
 12. The method of claim 7 wherein the first and second reducing atmospheres are selected from the group comprising forming gas, ammonia, dry hydrogen.
 13. The method of claim 7 and comprising: e) annealing the densified body in a reducing atmosphere.
 14. A method for producing a cermet composition, comprising: a) mixing a first predetermined amount of a yttria stabilized zirconia powder with between 2 and 8 weight percent mu-metal powder to define a homogeneous admixture; b) oxidizing the mu-metal in the admixture; c) forming the homogeneous admixture into a green body; d) calcining the green body in a first reducing atmosphere to remove oxygen from the oxidized mu-metal to yield a calcined body; and e) sintering the calcined body in a second reducing atmosphere to yield a densified body having no more than 0.8% porosity; wherein the densified body has a plurality of mu-metal particles distributed therethrough; wherein the densified body has a hardness of at least 1450 HV; wherein the densified body has a flexural strength of at least 200 kPSI; and wherein the densified body has a relative permeability μ/μ_(o) of at least
 850. 15. The method claim 14 wherein the densified body has between 3 and 5 weight percent mu-metal.
 16. The method claim 14 wherein the densified body has no more than 0.5 percent porosity.
 17. The method claim 14 wherein the densified body has no more than 0.2 percent porosity.
 18. The method claim 14 wherein the densified body has substantially zero porosity. 